1. Field of the Invention
The present invention relates generally to a wireless communication system, and in particular, to a multi-mode duplexing method for efficient resource management in a wireless communication system.
2. Description of the Related Art
Typically, there are two duplexing techniques: Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). In TDD, the same frequency band is divided into time slots and transmission and reception are alternately switched in time, for bi-directional communication. FDD provides bi-directional communication by dividing a given frequency band into a transmission band and a reception band.
A TDD communication system allocates time slots (or parts thereof) available to an Access Point (AP), to a user. This variable time slot allocation method enables asymmetrical communications. However, as a cell radius increases, a Round Trip Delay (RTD) increases the guard band between transmission time slots and reception time slots. As a result, transmission efficiency decreases. Accordingly, TDD is not feasible for a communication environment using a large cell radius like a macro cell. Moreover, since each cell does not use the same asymmetry rate in a multi-cell environment, serious frequency interference occurs between terminals at the boundary between neighboring cells.
An FDD communication system does not suffer a time delay in transmission or reception because a frequency band is divided for transmission and reception. Due to the absence of a time delay-caused RTD, FDD is suitable for the large cell radius environment like a macro cell. However, because of its fixed transmission and reception frequency bands, FDD is not feasible for asymmetrical transmission.
The 3rd Generation (3G) and future-generation mobile communication systems aim at providing concurrent provisioning of multimedia services with different traffic characteristics such as broadcasting and real-time video conferencing, in addition to traditional voice service. To efficiently provide these various services, duplexing techniques which consider the asymmetry and continuity of uplink and downlink transmission according Quality of Service (QoS), have been proposed.
FIG. 1 illustrates a conventional dual-band duplexing technique. In the conventional dual-band duplexing technique, an AP switches between a transmission mode and a reception mode on two frequency band channels, i.e., a broadband channel and a narrow band channel every predetermined same period. Access Terminals (ATs) connected to the AP operate in the opposite mode to that of the AP and are allocated resources for reception and transmission on the two frequency band channels such that they do not overlap.
In other words, AT #1 and AT #2 occupy two equal halves of a broadband channel 101a that the AP uses in transmission mode, during reception mode intervals 101a-1 and 101a-2, respectively. AT #3 and AT #4 partially occupy a narrow band channel 103a that the AP uses for transmission, during reception mode intervals 103a-2 and 103a-1, respectively. AT #1 and AT #4 occupy part of a broadband channel 101b that the AP uses in reception mode, during transmission mode intervals 101b-1 and 101b-2, respectively. AT #2 and AT #3 partially occupy a narrow band channel 103b that the AP uses for reception, during transmission mode intervals 103b-2 and 103b-1, respectively.
This dual-band duplexing technique suffers loss of the symmetry between uplink and downlink channels due to switching between bands. Also, it is difficult to control uplink and downlink resource rates according to traffic condition, and a multi-mode MODEM is required to support a plurality of bands, thereby increasing a terminal's manufacturing cost.
FIG. 2 illustrates a band switching duplexing technique. The uplink and downlink are switched in one band every predetermined period T (sec). Alongside TDD channel switching, different bands are used for the uplink and downlink, simultaneously.
However, the use of the same-band channels decreases flexibility of resource allocation (i.e. control of uplink and downlink resource rates) and channels are periodically switched. Therefore, asymmetric transmission is difficult to implement.